Valve with increased inlet flow

ABSTRACT

A check valve having a profiled entrance that reduces net positive suction head for piston and plunger pumps. The valve inlet surface has a cross-section that may include a curved portion that corresponds to a portion of a cone, circle, ellipse, hyperbola, or parabola.

TECHNICAL FIELD OF THE INVENTION

[0001] The invention generally relates to check valves used in pumpingoperations. More specifically, the invention relates to a check valvewith a profiled entrance for reducing net positive suction head forpiston and plunger pumps.

BACKGROUND OF THE INVENTION

[0002] Check valves are devices that allow fluid to flow through apassageway in one direction but block flow in the reverse direction. Theforce of gravity and/or the action of a spring aids in closing thevalve. FIG. 1 shows an example of a conventional check valve assembly.As shown therein, the major components of a check valve include: a valvebody 16, a spring retainer 17, a valve 18, and biasing member 12 incompression between the valve and the spring retainer.

[0003] Check valves are used in a variety of applications, fromregulating flow in HPLC machines to downhole drilling operations.Because check valves are used universally, in many types of media, theyare prone to damage, including stuck or missing discs, backstop tapping,seat tapping, disc flutter, disc stud pin wear, hinge pin wear, and flowleakage. One of the major problems occurring with check valves withoutsufficient suction head(pressure), is cavitation.

[0004] Cavitation is the process in which a liquid changes to a vapordue to a reduction in pressure below liquid vapor pressure. Currently,almost all check valves for piston and plunger pumps have sharp cornersat valve entrances or have a very small chamfer or radius, just enoughto break the sharp corner. The result of this configuration is venacontracta. Vena contracta is defined as the contracted portion of aliquid jet at and near the orifice from which it issues. The fluidstream 50 shown in FIG. 2 contracting through a minimum diameter 51, isthe prime mover for cavitation at check valve inlets. The sharp edges 52in the entrance 53 cause flow separation, which results innon-recoverable pressure loss. Basically, the sudden increase in thevelocity of the pumped liquid as fluid passes from a large flow area toa smaller flow area reduces the inlet pressure, sometimes below theliquid vapor pressure, resulting in the formation of gas and bubbles.The bubbles are caught up and swept upward along the inside cavity.Somewhere along the cavity, the pressure may once again drop below thevapor pressure and cause the bubbles to collapse. Implosions of thesevapor pockets can be so rapid that a rumbling/cracking noise isproduced. The hydraulic impacts of the shock waves caused by thecollapsing bubbles are strong enough to cause minute areas of fatigue onthe metal piston or plunger surfaces. Depending on the severity of thecavitation, a decrease in pump performance may also be noted. Cavitationdamage to the pump may range from minor pitting to catastrophic failureand depends on the pumped fluid characteristics, energy levels, andduration of cavitation.

[0005] Thus, if the suction head of a given pump, namely the energy perlb. (due to pressure, velocity or elevation) required by a liquid toremain a fluid, cannot be raised above the vaporization line bydecreasing the temperature or increasing the pressure, cavitation willoccur. Cavitation often occurs on pumps in offshore platforms due tospace constraints; there is not room available for equipment to houselarge flow regions, which would allow for minimal pressure reduction,thereby reducing the risk of cavitation. Instead, the equipment promotessmall flow regions with many pressure drops, leading to frequentcavitation and premature damage of fluid end components.

[0006] The first reaction to a cavitation problem is typically to checkthe net positive suction head available (NPSHa), measured at the suctionflange, and compare it to the net positive suction head required(NPSHr). The NPSHa is a characteristic of the system and is defined asthe energy which is in a liquid at the suction connection of the pumpover and above that energy in the liquid due to its vapor pressure. TheNPSHr is a characteristic of the pump design. It is determined by testor computation and is the energy needed to fill a pump on the suctionside and overcome the friction and pressure losses from the suctionconnection to that point in the pump at which more energy is added; theNPSHr is the minimum head required to prevent cavitation with a givenliquid at a given flowrate. The ratio of NPSHa/NPSHr must besufficiently large to prevent formation of cavitation bubbles.

[0007] Normally, the NPSHr plotted on the traditional pump curve isbased on a 3% head loss due to cavitation, a convention established manyyears ago in the Hydraulic Institute of Standards. Permitting a headloss this large means that at some higher flow condition cavitationwould already have begun before performance loss was noticed.

[0008] For this reason, it is imperative that a margin be providedbetween the NPSHr and the NPSHa at the desired operating conditions.Further, the NPSHr will actually tend to increase with a reduction inflow.

[0009] A reasonable margin of 8 ft of water at rated flow rate iscommonly accepted by end users for most services. For known problemapplications, such as vacuum tower bottoms and some solvents, thismargin is often increased to 10 ft.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention is a check valve that includes a profiledentrance for reducing net positive suction head required. Profiled isdefined as being shaped into a particular, predetermined form tostreamline flow and minimize vena contracta. The profiled entranceoffers an improvement over traditional sharp-cornered entrances byallowing the nozzle to require a lower pressure at the same flow rate.By requiring a lower inlet pressure, the total pressure loss in the pumpis reduced, which in turn, reduces the net positive suction headrequired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more detailed understanding of the present invention,reference is made to the following Figures, wherein:

[0012]FIG. 1 is a schematic representation of a typical, check valvewith a sharp-cornered entrance (prior art).

[0013]FIG. 2 is a schematic representation of vena contracta;

[0014]FIG. 3 is an assembly drawing of a check valve constructed inaccordance with a preferred embodiment, having a rounded entrance,single radius;

[0015]FIG. 4 is an assembly drawing of a first alternative embodiment ofthe present check valve, having a rounded entrance, double radii;

[0016]FIG. 5 is an assembly drawing of a second alternative embodimentof the present check valve, having a conical entrance;

[0017]FIG. 6 is an assembly drawing of a third alternative embodiment ofthe present check valve, having a taper entrance;

[0018]FIG. 7 is a representative drawing of an ellipse;

[0019]FIG. 8 is an assembly drawing of a fourth alternative embodimentof the present check valve, having an elliptical entrance;

[0020]FIG. 9 is a representative drawing of a hyperbola;

[0021]FIG. 10 is an assembly drawing of a fifth alternative embodimentof the present check valve, having a hyperbolic entrance;

[0022]FIG. 11 is a representative drawing of a parabola; and

[0023]FIG. 12 is an assembly drawing of a sixth alternative embodimentof the present check valve, having a paraboloidal entrance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024]FIG. 1 is a cross-section of a check valve assembly 10 containing:a valve body 16 having a bore therethrough, the bore having an inlet 30and an outlet 11, a valve 18 engaging body 16 at outlet 11, a springretainer 17 engaging body 16 and surrounding valve 18 and outlet 11, avalve seat 13; a first biasing member 12 in compression between body 16and spring retainer 17; and a second biasing member 15 in compressionbetween body 16 and valve 18. The prior art typically has a smallchamfer 31 in the valve body at the inlet 30. Valve assembly 10 has alongitudinal axis 99.

[0025] The valve is designed to open and allow fluid passage when theforce of the working fluid in the positive flow direction 32 exceeds thecompressive load of biasing member 12 (shown as a coil spring), whichmaintains valve 18 against valve seat 13. If the flow pressure decreasesor reverses in direction, biasing spring 12 will act to close valve 18against valve seat 13 and prevent reverse fluid flow.

[0026] FIGS. 3-6, 8, 10, and 12 are alternative embodiments of checkvalves in accordance with the present invention. The check valvesinclude all the components of FIG. 1, except chamfer 31 in the valvebody at inlet 30. In each embodiment, the valve body at inlet 30 hasbeen modified to minimize vena contracta.

[0027]FIG. 3 is a cross-section of a check valve assembly with a roundedinlet surface 60 and an inlet diameter 61. Inlet surface 60 has a singleradius of curvature 62. The radius of curvature 62 is preferably limitedby R≧0.05 D, where R is radius 62 and D is diameter 61.

[0028]FIG. 4 is a cross-section of a check valve assembly with a curvedinlet surface 70 and a diameter 73. Curved inlet surface 70 is acontinuous curve having a radius of curvature that ranges from radius ofcurvature 71 to radius of curvature 72. The radii 71 and 72 arepreferably each limited by R≧0.05D, where R is radius 71 or 72 and D isdiameter 73.

[0029]FIG. 5 is a cross-section of a check valve assembly with afrustoconical inlet surface 81 having a height 80 and an inner diameter82. An angle a is defined between surface 81 and axis 99 and ispreferably between 10° and 75°. The ratio of height 80 to inner diameter82 is preferably greater than 0.05.

[0030]FIG. 6 is a cross-section of a check valve assembly with a taperedinlet having a frustoconical inlet surface 90. Unlike surface 80 in FIG.5, surface 90 extends inward all the way to valve disk 18. An angle γ isdefined between surface 90 and axis 99 and is preferably between 5° and75°.

[0031]FIG. 7 is a cross-section of a representative ellipse 105. Ellipse105 is vertical and defined by the equation y²/a²+x²/b²=1 wherein a is avalue on major axis 106 and b is a value on minor axis 107. For anellipse having its center at the origin (0, 0), the foci c are definedby a²−b²=c². The major axis is on the y-axis and has a length of 2 a.The minor axis is on the x-axis and has a length of 2 b. The foci arelocated at (0, c) and (0, −c). The vertices are at (0, a) and (0, −a).The convertices are at (b, 0) and (−b, 0).

[0032]FIG. 8 is a cross-section of a check valve assembly wherein thecross-section of inlet mouth 102 is defined by one quadrant of anellipse 101. The inlet mouth has an inner diameter, d, 100 and an outerdiameter, D, 130. Ellipse 101 is defined by the same equation as ellipse105 of FIG. 7. Thus, ellipse 101 is characterized by major and minoraxis 103 and 104, respectively, of which major axis 103 is parallel toinlet axis 99. In a preferred embodiment, 103 is ≧0.05D and 104 is≧0.05(D-d) and 0.05d.

[0033]FIG. 9 shows a representative hyperbola 115. Hyperbola 115 isvertical and defined by equation x²/a²−y²/b²=1 wherein a is a value ontransverse axis 116, b is a value on conjugate axis 117. The center isat point (0, 0). The asymptotes are at y=(b/a)x and (−b/a)x. Thevertices are at (a, 0) and (−a, 0). The foci are at (c, 0) and (−c, 0)where a, b, and c are related by c²=a²+b². The transverse axis is on thex-axis and has a length of 2 a. The conjugate axis is on the y-axis andhas a length of 2 b.

[0034]FIG. 10 is a cross-section of a check valve assembly wherein thecross-section of inlet mouth 112 is defined by a portion of hyperbola111 and the inlet mouth has an inner diameter, D, 110. Hyperbola 111 isdefined by the same equation as hyperbola 115 of FIG. 9 and ispositioned such that transverse axis 113 defines an angle φ with respectto the inlet axis 99. In the embodiment shown φ is 45°. In otherpreferred embodiments, φ is preferably between 0° and 90° and a and bare ≧0.01D.

[0035]FIG. 11 shows representative parabola 125. Parabola 125 isvertical and defined by the equation x=4py wherein p is the focus of theparabola located on the y-axis 126. The vertex 127 is located at point(0, 0). The focus is at (0, p). The directrix is at y=−p. The quantity4p is known as the latus rectum 4p.

[0036]FIG. 12 is a cross-section of a check valve assembly wherein thecross-section of inlet mouth 123 is partially defined by a portion of aparabola 121 and has an inner diameter, D, 120. In the embodiment shown,the inlet surface defines one-half of parabola 121. Parabola 121 isdefined by the same equation as parabola 125 of FIG. 11 and ischaracterized by y-axis 124 and x-axis 123. In a preferred embodiment,y-axis 124 is parallel to inlet axis 99. In other embodiments, y-axis124 can be at an angle of from 0° to 90° degrees with respect to inletaxis 99, and p is ≧0.01D.

[0037] Reducing the pressure loss due to vena contracta is advantageousfor a number of reasons. First of all, by profiling the body of thevalve at the inlet, the change in velocity of the pumped liquid as fluidpasses from a large flow area to a smaller flow is reduced. This isbecause the liquid undergoes a gradual flow change, which results in asmaller reduction in the inlet pressure. If the change in the inletpressure is kept to a minimum, the required pump suction head will bemet, and cavitation cannot occur.

[0038] In order to prove that pressure loss due to vena contracta can bereduced by simply changing the shape of the valve body at the inlet, thefollowing experiments were conducted using nozzles. A check valve inletin a pump can be viewed as a nozzle because the valve seat is short andthe through bore diameter is smaller than the fluid end chamberdiameter.

EXAMPLE 1

[0039] Experiment

[0040] Nozzles were made to ⅛ scale of the actual valve size todetermine profiled inlet's effects on pressure and through flow volume.The new profile selected was the rounded inlet with a single radius,shown in FIG. 3.

[0041] Results: Flow Rate

[0042] Some of the test results are shown on Table 1. It is clear thatmore flow goes through the nozzle with the new profiled inlet than thenozzle with the standard sharp corner inlet at the same pressure. Onaverage, there is a 27.4% increase in fluid flow at an average 25.33 gpmthrough the new profiled inlet, as compared to the standard inlet.

[0043] Results: Pressure

[0044] Still looking at Table 1, it is clear that lower pressure isrequired by the profiled inlet nozzle than the standard nozzle at thesame flow rate. On average, there is a 34.9% reduction in pressure lossat an average 12.83 gpm through the new profiled inlet, as compared tothe standard inlet. TABLE 1 Flow Rate @ Flow Rate @ Flow Rate @ Pressure@ Pressure @ 30 psi 26 psi 20 psi 12.22 gpm 13.44 gpm Standard 13.06 gpm12.07 gpm 10.57 gpm 26 psi 32 psi New Profile 16.46 gpm 15.32 gpm 13.67gpm 16 psi 20 psi Improvement 26.0% 26.9% 29.3% 38.5% 31.3%

EXAMPLE 2

[0045] Experiment

[0046] Based on the results from Experiment 1, valves were made toactual size with new profile inlets, and tested in a pump driven by anengine to determine the profiled inlet's effect on cavitation.

[0047] Results: Cavitation

[0048] Results are shown on Table 2. With a standard valve, the pumpstarts to cavitate at an engine speed of 1450 rpm, and is severelycavitating at 1500 rpm. However, with a new profiled valve, the pumpstarts to cavitate at 1550 rpm and only slightly cavitates above 1550rpm. TABLE 2 Engine Speed (rpm) Observations Standard 1450 Starts tocavitate at 1450 rpm; at 1500 rpm, very bad cavitation New Profile 1550Starts to cavitate at 1550 rpm

[0049] The embodiments described herein are exemplary only, and are notlimiting. Many variations and modifications of the invention and theprinciples discussed herein are possible and are within the scope of theinvention. Accordingly, the scope of protection is not limited by thedescription set out above, but is only limited by the claims thatfollow, that scope including all equivalents of the subject matter ofthe claims.

What is claimed is:
 1. A check valve for controlling the flow of liquidunder high pressure, wherein the valve comprises: a valve body having aborethrough, said bore having an inlet and an out let; a valve engagingsaid body at said outlet; a spring retainer engaging said body andsurrounding said valve and said outlet; a biasing member in compressionbetween said valve and said spring retainer; and said body having aprofiled inlet, wherein said inlet has a rounded inlet with a singleradius.
 2. The check valve assembly of claim 1 wherein said radius isdefined by a relationship with the diameter of the bore according to theequation R≧0.05, where R is the radius of the rounded inlet and D is thediameter of the bore.
 3. A check valve for controlling the flow ofliquid under high pressure, wherein the valve comprises: a valve bodyhaving a borethrough, said bore having an inlet and an out let; a valveengaging said body at said outlet; a spring retainer engaging said bodyand surrounding said valve and said outlet; a biasing member incompression between said valve and said spring retainer; and said bodyhaving a profiled inlet, wherein said inlet has a rounded inlet with tworadii.
 4. The check valve assembly of claim 3 wherein said radii aredefined by a relationship with the diameter of the bore according to theequation R≧0.05D, where R is the radius of both rounded segments of theentrance and D is the diameter of the bore.
 5. A check valve forcontrolling the flow of liquid under pressure, wherein the valvecomprises: a valve body having a borethrough, said bore having an inletand an out let; a valve engaging said body at said outlet; a springretainer engaging said body and surrounding said valve and said outlet;a biasing member in compression between said valve and said springretainer; and said body having a profiled inlet, wherein said inlet hasa conical entrance with angle α.
 6. The check valve assembly of claim 5wherein said angle α is defined by the limitation α=10°-75° and theheight/diameter ratio of the entrance is defined by height/diameter≧0.05.
 7. A check valve for controlling the flow of liquid under highpressure, wherein the valve comprises: a valve body having aborethrough, said bore having an inlet and an out let; a valve engagingsaid body at said outlet; a spring retainer engaging said body andsurrounding said valve and said outlet; a biasing member in compressionbetween said valve and said spring retainer; and said body having aprofiled inlet, wherein said inlet has a tapered entrance with angle γ.8. The check valve assembly of claim 7 wherein said angle γ is definedby the limitation γ=5°-75°.
 9. A check valve for controlling the flow ofliquid under high pressure, wherein the valve comprises: a valve bodyhaving a borethrough, said bore having an inlet and an outlet; a valveengaging said body at said outlet; a spring retainer engaging said bodyand surrounding said valve and said outlet; a biasing member incompression between said valve and said valve retainer; and said bodyhaving a profiled inlet, wherein said inlet has an elliptical entrance.10. A check valve for controlling the flow of liquid under highpressure, wherein the valve comprises: a valve body having aborethrough, said bore having an inlet and an out let; a valve engagingsaid body at said outlet; a spring retainer engaging said body andsurrounding said valve and said outlet; a biasing member in compressionbetween said valve and said spring retainer; and said body having aprofiled inlet, wherein said inlet has a hyperbolic entrance.
 11. Acheck valve for controlling the flow of liquid under high pressure,wherein the valve comprises: a valve body having a borethrough, saidbore having an inlet and an out let; a valve engaging said body at saidoutlet; a spring retainer engaging said body and surrounding said valveand said outlet; a biasing member in compression between said valve andsaid spring retainer; and said body having a profiled inlet, whereinsaid inlet has a paraboloidal entrance.